A typical catalytic combustion apparatus oxidizes a gaseous fuel, such as methane, butane or propane, at room temperature to generate heat. Generally, the fuel is introduced into a gas-tight housing where the fuel expands to completely fill the housing. As the fuel diffuses through a catalyst-containing support located at an outlet of the housing, ambient air mixes with the diffused fuel. The fuel-air mixture is then oxidized by a reaction promoted by the catalyst to produce heat. Such catalysts typically include noble metals such as platinum group metals or compounds containing the same. The substrates upon which the catalysts are supported are typically made from glass fibers, porous metals or ceramics such as ceramic wool or ceramic board and the like.
The products of the catalyst-enhanced oxidation reaction, such as carbon dioxide and water vapor, are discharged through the outside surface of the catalyst-containing substrate. Convection currents disperse the reaction products and draw in ambient air to provide oxygen to sustain the reaction. The reaction is normally started by igniting the reactants, by means of a flame (e.g. a pilot light) or a spark induced, for example, by an electrical ignition.
A drawback of such known combustion apparatuses is reliance on convection currents to circulate the reactants (air and fuel) and to remove combustion products from the catalyst-containing reaction zone. A factor which contributes to controlling the rate of oxygen available per unit area of catalyst is the rate of convection flow over the active catalytic surface. Convection currents often produce irregular and erratic flows of reactants over the active catalytic surface. Under such conditions, there is typically an uneven distribution of oxygen and/or fuel within the reaction zone containing the catalyst. Consequently, when oxygen is available in less than a stoichiometric amount relative to the fuel, incomplete combustion of the fuel occurs resulting in harmful by-products including carbon monoxide, unburned fuel and the like. As carbon monoxide and unreacted fuel accumulate, a dangerous health hazard arises that could result in serious injury or death to occupants of an enclosed space in which the heating apparatus is used.